1. Field of the Invention
This invention relates to the reduction of the air reactivity of calcined petroleum coke.
2. Background
Petroleum coke is generally produced commercially by charging a heavy petroleum residuum stream to a coking drum at an elevated temperature, typically from about 800.degree. F. to about 900.degree. F., until the drum is filled and the heavy petroleum residuum has been converted to petroleum coke. As the coke forms in the coking drum, the heavy petroleum residuum decomposes into petroleum coke which is recovered from the coking drum by the use of high-impact-producing water jets which are used to drill the petroleum coke from the coke drum. The coke typically falls into a coke pit from which it is recovered and passed to coke storage, and thereafter to coke calcining to produce the calcined petroleum coke. In this process water streams contact the petroleum coke in the form of the high-pressure water used to drill the petroleum coke from the coking drum, in the coke pit where the petroleum coke is collected as well as in coke coolers which typically comprise rotary coolers which use a water stream to cool the coke from typical calcining temperatures of about 2000.degree. F. to about 100.degree. F. or spray coolers. Frequently, an aqueous sodium hydroxide stream is used to scrub the off-gases from the coke calciner to produce a clean off-gas stream. Such processes are considered to be well-known to the art and representative processes are disclosed in U.S. Pat. No. 3,917,564, issued Nov. 4, 1975 to Meyers and assigned to Mobil Oil Corporation; U.S. Pat. No. 4,334,981, issued Jun. 15, 1982 to Holloway et al and assigned to Atlantic Richfield Company; U.S. Pat. No. 4,547,284, issued Oct. 15, 1985 to Sze et al and assigned to Lummus Crest Inc.; U.S. Pat. No. 4,666,585, issued May 19, 1987 to Figgins et al and assigned to Atlantic Richfield Company; and U.S. Pat. No. 4,968,407, issued Nov. 6, 1990 to McGrath et al and assigned to Foster Wheeler USA Corporation, all of which are hereby incorporated in their entirety by reference.
In such processes, the resulting calcined petroleum coke frequently has an air reactivity from about 0.2 to about 0.3 weight percent per minute. Air reactivity is generally determined by a test comprising heating the calcined petroleum coke to an elevated temperature such as, for instance, about 600.degree. F. and passing air over the heated sample of calcined petroleum coke. The air reactivity represents the weight percent loss per minute as a result of reaction with air at the elevated temperatures.
Many users of calcined petroleum coke wish the air reactivity to be from about 0.1 to about 0.15 weight percent per minute or less.
As a result, a continuing effort has been directed to the development of methods for the production of calcined petroleum coke which result in the production of calcined petroleum coke having a reduced air reactivity.